Method for reducing tip-to-tip spacing between lines

ABSTRACT

This invention provides a method for reducing tip-to-tip spacing between lines using a combination of photolithographic and copolymer self-assembling lithographic techniques. A mask layer is first formed over a substrate with a line structure. A trench opening of a width d is created in the mask layer. A layer of a self-assembling block copolymer is then applied over the mask layer. The block copolymer layer is annealed to form a single unit polymer block of a width or a diameter w which is smaller than d inside the trench opening. The single unit polymer block is selectively removed to form a single opening of a width or a diameter w inside the trench opening. An etch transfer process is performed using the single opening as a mask to form an opening in the line structure in the substrate.

FIELD OF THE INVENTION

This invention relates to a photolithography process for semiconductorfabrication. More particularly, this invention is directed to a methodfor reducing tip-to-tip spacing between lines using a combination ofphotolithographic and copolymer self-assembling lithographic techniques.

BACKGROUND OF THE INVENTION

Photolithography is commonly used to make miniaturized electroniccomponents such as integrated circuits in semiconductor manufacturing.In a photolithography process, a layer of photoresist is deposited on asubstrate, such as a silicon wafer. The substrate is baked to remove anysolvent remained in the photoresist layer. The photoresist is thenselectively exposed through a photomask with a desired pattern to asource of actinic radiation. The radiation exposure causes a chemicalreaction in the exposed areas of the photoresist and creates a latentimage corresponding to the mask pattern in the photoresist layer. Thephotoresist is next developed in a developer solution to remove eitherthe exposed portions of the photoresist for a positive photoresist orthe unexposed portions of the photoresist for a negative photoresist.The patterned photoresist can then be used as a mask for subsequentfabrication processes on the substrate, such as deposition, etching, orion implantation processes.

Advances in semiconductor device performance have typically beenaccomplished through a decrease in semiconductor device dimensions. Itis known that the tip-to-tip spacing between lines (e.g., PC lines) hasa high impact on the unit cell density of the semiconductor device.Reducing the tip-to-tip distance between lines will greatly increase theunit cell density which in turn will lead to a shrinkage in the devicedimension. However, due to the line end shortening issue and theresolution limitation of photolithography, the currently availablelithographic techniques can only achieve a tip-to-tip distance of notless than 100 nm.

It has been known that certain materials are capable of organizing intoordered structures without the need for human interference, which isreferred to as the self-assembly of materials. Self-assembling copolymerlithographic techniques have been developed to form useful periodicpatterns with dimensions in the range of 10 to 40 nm. Eachself-assembling block copolymer system contains two or more differentpolymeric block components which are immiscible with one another. Undersuitable conditions, these polymeric block components can separate intotwo or more different phases on a nanometer-scale and thereby formordered nano-sized patterns. Such ordered patterns can be used forfabricating nano-scale structural units in semiconductor, optical andmagnetic devices.

However, the complementary metal oxide semiconductor (CMOS) technologyrequires precise placement or registration of individual structuralunits to form metal lines and vias in the wiring level. The large,ordered array of repeating structural units formed by self-assemblingblock copolymers cannot be used in the CMOS technology, because of thelack of alignment or registration of the positions of individualstructural units.

SUMMARY OF THE INVENTION

The present invention provides a method for reducing tip-to-tip spacingbetween lines using a combination of photolithographic and copolymerself-assembling lithographic techniques.

In one aspect, the present invention relates to a method for reducingtip-to-tip spacing between lines involving the steps of providing asubstrate and a line structure in the substrate; forming a mask layerover the substrate; performing a lithographic process over the masklayer to create a trench opening of a width d in the mask layer, whereinthe trench opening is above the line structure in the substrate andperpendicular to the line structure; applying a layer of a blockcopolymer over the mask layer, wherein the block copolymer comprises atleast first and second polymeric block components A and B respectivelythat are immiscible with each other; annealing the block copolymer layerto form a single unit polymer block of a width or a diameter w insidethe trench opening, wherein w<d, and wherein the single unit polymerblock comprises the polymeric block component B and is embedded in apolymeric matrix that comprises the first polymeric block component A;selectively removing the second polymeric block component B to form asingle opening of a width or a diameter w in the polymeric matrix insidethe trench opening; and performing an etch transfer process using thesingle opening as a mask to form an opening in the line structure in thesubstrate.

In another aspect, the present invention relates to a method forreducing tip-to-tip spacing between lines involving the steps ofproviding a substrate and a line structure in the substrate; forming afirst mask layer over the substrate; forming a second mask layer overthe first mask layer; performing a lithographic process over the secondmask layer to create a trench opening of a width d in the second masklayer, wherein the trench opening is above the line structure in thesubstrate and perpendicular to the line structure; applying a layer of ablock copolymer over the second mask layer, wherein the block copolymercomprises at least first and second polymeric block components A and Brespectively that are immiscible with each other; annealing the blockcopolymer layer to form a single unit polymer block of a width or adiameter w inside the trench opening, wherein w<d, and wherein thesingle unit polymer block comprises the polymeric block component B andis embedded in a polymeric matrix that comprises the first polymericblock component A; selectively removing the second polymeric blockcomponent B to form a single opening of a width or a diameter w in thepolymeric matrix inside the trench opening; performing a first etchtransfer process using the single opening as a mask to form an openingin the first mask layer; and performing a second etch transfer processusing the opening in the first mask layer as a mask to form an openingin the line structure in the substrate.

The present invention may further involves the steps of forming anunderlayer over the substrate before forming the mask layer or layers;and stripping any remaining block copolymer layer, mask layer or layers,and underlayer, after performing the etch transfer process or processes.

The block copolymer of the present invention, when placed and annealedon a planar surface, self-assemblies into an ordered array of multipleunit polymer blocks embedded in the polymeric matrix, wherein each ofthe multiple unit polymer blocks has the width or diameter w, and themultiple unit polymer blocks are spaced apart from each other in theordered array by a distance s.

When 0.6 (w+s)<d<1.5 (w+s), a single unit polymer block is formed insideand self-aligned to the trench opening. For example, when w ranges fromabout 10 nm to about 50 nm and s ranges from about 10 nm to about 60 nm,d may range from about 40 nm to about 160 nm.

The annealing of the block copolymer is preferably, but not necessarily,conducted at a temperature from about 130° C. to about 230° C. Thepreferred annealing time is from about 40 minutes to about 80 minutes.The thickness of the block copolymer layer is preferably from about 15nm to about 45 nm.

The block copolymer preferably comprises the first and second polymericblock components A and B at a weight ratio of from about 60:40 to about40:60, and wherein the single unit polymer block comprises a lamellathat stands perpendicular to the upper surface of said line structure.

Suitable block copolymers that can be used in the present inventioninclude, but are not limited to:polystyrene-block-polymethylmethacrylate (PS-b-PMMA),polystyrene-block-polyisoprene (PS-b-PI),polystyrene-block-polybutadiene (PS-b-PBD),polystyrene-block-polyvinylpyridine (PS-b-PVP),polystyrene-block-polyethyleneoxide (PS-b-PEO),polystyrene-block-polyethylene (PS-b-PE),polystyrene-block-polyorganosilicate (PS-b-POS),polystyrene-block-polyferrocenyldimethylsilane (PS-b-PFS),polyethyleneoxide-block-polyisoprene (PEO-b-PI),polyethyleneoxide-block-polybutadiene (PEO-b-PBD),polyethyleneoxide-block-polymethylmethacrylate (PEO-b-PMMA),polyethyleneoxide-block-polyethylethylene (PEO-b-PEE),polybutadiene-block-polyvinylpyridine (PBD-b-PVP), andpolyisoprene-block-polymethylmethacrylate (PI-b-PMMA).

Other aspects, features and advantages of the invention will be morefully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1A shows a three-dimensional view of a pattern that is formed by ablock copolymer with first and second polymeric block components A andB, while the pattern comprises an ordered array of lamellae composed ofthe polymeric block component B in a polymeric matrix composed of thepolymeric block component A.

FIG. 1B shows the top view of the pattern of FIG. 1A.

FIG. 2A shows a three-dimensional view of a pattern that is formed by ablock copolymer with first and second polymeric block components A andB, while the pattern comprises an ordered array of cylinders composed ofthe polymeric block component B in a polymeric matrix composed of thepolymeric block component A.

FIG. 2B shows the top view of the pattern of FIG. 4A.

FIG. 3 illustrates the dimensions of the ordered array of lamellae andthe relative dimensions of a lithographic feature that can be used forprecise placement of a single cylinder.

FIG. 4 illustrates the dimensions of the ordered array of cylinders andthe relative dimensions of a lithographic feature that can be used forprecise placement of a single cylinder.

FIGS. 5A-13B are cross-sectional and top views that illustrate exemplaryprocessing steps for reducing tip-to-tip spacing between lines accordingto one embodiment of the present invention.

FIGS. 14A-23B are cross-sectional and top views that illustrateexemplary processing steps for reducing tip-to-tip spacing between linesaccording to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In describing the preferred embodiments of the present invention,reference will be made herein to FIGS. 1A-23B of the drawings in whichlike numerals refer to like features of the invention. Features of theinvention are not necessarily shown to scale in the drawings.

It is understood that when an element, such as a layer, region orsubstrate, is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements may also bepresent.

The present invention combines the conventional photolithographytechnology with the copolymer self-assembling lithographic techniques toreduce tip-to-tip spacing between lines.

Specifically, a mask layer is first formed over the substrate containinga line structure. A trench opening is then created in the mask layer byconventional lithography and etch techniques. Such a trench opening hasa relatively large width d which is consistent with the resolutions ofthe conventional lithography technology. It is preferred that the trenchopening is above the line structure in the substrate and perpendicularto the line structure. A thin layer of a self-assembling block copolymeris then applied over the mask layer. The block copolymer layerpreferably has a thickness ranging from about 10 nm to about 50 nm, morepreferably from about 15 nm to about 45 nm. The self-assembling blockcopolymer is annealed to form an ordered pattern. The width of thetrench opening is carefully selected so that only a single unit polymerblock can be formed inside the trench opening. The single unit polymerblock is embedded in a polymeric matrix and has a width or diameter of wwhich is smaller than the width of the trench opening. The single unitpolymer block can be selectively removed to form a single opening of awidth or diameter of w in the polymeric matrix inside the trenchopening. The single opening can then be used as a mask to form anopening in the line structure in the substrate.

There are many different types of block copolymers that can be used forpracticing the present invention. As long as a block copolymer containstwo or more different polymeric block components that are not immisciblewith one another, such two or more different polymeric block componentsare capable of separating into two or more different phases on ananometer scale and thereby form patterns of isolated nano-sizedstructural units under suitable conditions.

In a preferred, but not necessary, embodiment of the present invention,the block copolymer consists essentially of first and second polymericblock components A and B that are immiscible with each other. The blockcopolymer may contain any numbers of the polymeric block components Aand B arranged in any manner. The block copolymer can have either alinear or a branched structure. Preferably, such a block polymer is alinear diblock copolymer having the formula of A-B.

Specific examples of suitable block copolymers that can be used forforming the structural units of the present invention may include, butare not limited to: polystyrene-block-polymethylmethacrylate(PS-b-PMMA), polystyrene-block-polyisoprene (PS-b-PI),polystyrene-block-polybutadiene (PS-b-PBD),polystyrene-block-polyvinylpyridine (PS-b-PVP),polystyrene-block-polyethyleneoxide (PS-b-PEO),polystyrene-block-polyethylene (PS-b-PE),polystyrene-block-polyorganosilicate (PS-b-POS),polystyrene-block-polyferrocenyldimethylsilane (PS-b-PFS),polyethyleneoxide-block-polyisoprene (PEO-b-PI),polyethyleneoxide-block-polybutadiene (PEO-b-PBD),polyethyleneoxide-block-polymethylmethacrylate (PEO-b-PMMA),polyethyleneoxide-block-polyethylethylene (PEO-b-PEE),polybutadiene-block-polyvinylpyridine (PBD-b-PVP), andpolyisoprene-block-polymethylmethacrylate (PI-b-PMMA).

The specific structural units formed by the block copolymer aredetermined by the molecular weight ratio between the first and secondpolymeric block components A and B. For example, when the ratio of themolecular weight of the first polymeric block component A over themolecular weight of the second polymeric block component B is greaterthan about 80:20, the block copolymer will form an ordered array ofspheres composed of the second polymeric block component B in a matrixcomposed of the first polymeric block component A. When the ratio of themolecular weight of the first polymeric block component A over themolecular weight of the second polymeric block component B is less thanabout 80:20 but greater than about 60:40, the block copolymer will forman ordered array of cylinders composed of the second polymeric blockcomponent B in a matrix composed of the first polymeric block componentA. When the ratio of the molecular weight of the first polymeric blockcomponent A over the molecular weight of the second polymeric blockcomponent B is less than about 60:40 but is greater than about 40:60,the block copolymer will form alternating lamellae composed of the firstand second polymeric block components A and B. Therefore, the molecularweight ratio between the first and second polymeric block components Aand B can be readily adjusted in the block copolymer of the presentinvention, in order to form desired structural units.

In one preferred embodiment of the present invention, the ratio of themolecular weight of the first polymeric block component A over themolecular weight of the second polymeric block component B ranges fromabout 60:40 to about 40:60, so that the block copolymer of the presentinvention will form an ordered array of lamellae composed of the secondpolymeric block component B in a matrix composed of the first polymericblock component A, as shown in FIGS. 1A and 1B. Preferably, the secondpolymeric block component B can be selectively removable relative to thefirst polymeric block component A, thereby resulting in either isolatedand orderly arranged structural units composed of the un-removedcomponent, or a continuous structural layer containing isolated andorderly arranged cavities left by the removable component B.

In a particularly preferred embodiment of the present invention, theblock copolymer used for forming the self-assembled periodic patterns ofthe present invention is PS-b-PMMA with a PS:PMMA molecular weight ratioranging from about 60:40 to about 40:60.

In another preferred embodiment of the present invention, the ratio ofthe molecular weight of the first polymeric block component A over themolecular weight of the second polymeric block component B ranges fromabout 80:20 to about 60:40, so that the block copolymer of the presentinvention will form an ordered array of cylinders composed of the secondpolymeric block component B in a matrix composed of the first polymericblock component A, as shown in FIGS. 2A and 2B. Preferably, the secondpolymeric block component B can be selectively removable relative to thefirst polymeric block component A, thereby resulting in either isolatedand orderly arranged structural units composed of the un-removedcomponent, or a continuous structural layer containing isolated andorderly arranged cavities left by the removable component B.

In a particularly preferred embodiment of the present invention, theblock copolymer used for forming the self-assembled periodic patterns ofthe present invention is PS-b-PMMA with a PS:PMMA molecular weight ratioranging from about 80:20 to about 60:40.

In order to form the self-assembled periodic patterns, the blockcopolymer is first dissolved in a suitable solvent system to form ablock copolymer solution, which is then applied onto a surface to form athin block copolymer layer, followed by annealing of the thin blockcopolymer layer. The solvent system used for dissolving the blockcopolymer and forming the block copolymer solution may comprise anysuitable solvent, including, but not limited to: toluene, propyleneglycol monomethyl ether acetate (PGMEA), propylene glycol monomethylether (PGME), and acetone. The block copolymer solution preferablycontains the block copolymer at a concentration ranging from about 0.1%to about 2% by total weight of the solution. More preferably, the blockcopolymer solution contains the block copolymer at a concentrationranging from about 0.5 wt % to about 1.5 wt %. In a particularlypreferred embodiment of the present invention, the block copolymersolution comprises about 0.5 wt % to about 1.5 wt % PS-b-PMMA dissolvedin toluene or PGMEA.

The block copolymer solution can be applied to the surface of a devicestructure by any suitable techniques, including, but not limited to:spin coating, spraying, ink coating, and dip coating. Preferably, theblock copolymer solution is spin coated onto the surface of a substrateto form a thin block copolymer layer.

The substrate is then annealed to effectuate micro-phase segregation ofthe different block components contained by the block copolymer.Annealing of the self-assembling block copolymer in the presentinvention can be achieved by various methods known in the art,including, but not limited to: thermal annealing (either in a vacuum orin an inert atmosphere containing nitrogen or argon), ultra-violetannealing, laser annealing, solvent vapor-assisted annealing, orsupercritical fluid-assisted annealing.

In a preferred embodiment of the present invention, a thermal annealingstep is carried out to anneal the block copolymer layer at an elevatedannealing temperature that is above the glass transition temperature(T_(g)) of the block copolymer, but below the decomposition ordegradation temperature (T_(d)) of the block copolymer. Preferably, thethermal annealing step is carried out at an annealing temperature ofabout 100° C. to about 250° C. More preferably, the annealingtemperature is from about 130° C. to about 230° C. The thermal annealingmay last from about 30 minutes to about 10 hours, more preferably, fromabout 40 minutes to about 80 minutes.

The block copolymer, when applied and annealed on a planar surface,self-assembles into an ordered array of multiple structural unitscomprising said polymeric block component B embedded in a polymericmatrix comprising said first polymeric block component A. Each of saidmultiple structural units has a width or diameter w and is spaced apartfrom each other in the ordered array by a distance s (FIGS. 3 and 4).

In the present invention, the dimension of the trench opening in themask layer is adjusted so that only a single unit polymer block can beformed and placed inside the trench opening from the self-assemblingblock copolymer. In order to achieve formation and placement of such asingle structure unit inside the trench opening, it is preferred thatthe width of the trench opening d is more than 0.6 (w+s), but less than1.5 (w+s). For example, when w ranges from about 10 nm to about 50 nmand s ranges from about 10 nm to about 60 nm, d may range from about 40nm to about 160 nm.

FIGS. 5A-13B are cross-sectional and top views that illustrate exemplaryprocessing steps for reducing tip-to-tip spacing between lines accordingto one embodiment of the present invention.

FIG. 5A shows the cross-sectional view of a substrate 10 with a linestructure 12 on it. The cross-section site is across the line structure,as shown in FIG. 5B. The line structure is formed by any conventionallithography techniques. Preferably, the line structure is a gate linestructure. The substrate in the present invention is suitably anysubstrate conventionally used in lithography processes. For example, thesubstrate can be silicon, silicon oxide, aluminum-aluminum oxide,gallium arsenide, ceramic, quartz, copper or any combination thereofincluding multilayers.

A mask layer 16 is formed over the substrate 10, as shown in FIGS. 6Aand 6B. The mask layer 16 may comprise any suitable organic or inorganicphotosensitive materials that can be patterned by conventionallithography techniques. In a preferred embodiment, mask layer 16 is aphotoresist. More preferably, mask layer 16 is a Si-containingphotoresist. The mask layer may be applied by virtually any standardmeans including spin coating. The mask layer may be baked (PAB) toremove any solvent and improve the coherence of the mask layer. Thepreferred range of the PAB temperature is from about 70° C. to about150° C., more preferably from about 90° C. to about 130° C. A typicalbake time is from about 60 seconds to about 90 seconds. The preferredrange of thickness of the mask layer is from about 20 nm to about 400nm, more preferably from about 50 nm to about 300 nm.

Optionally, but not necessarily, an underlayer 14 may be applied overthe substrate 10 with the line structure 12 before the mask layer 16 isformed, as shown in FIGS. 7A and 7B. The underlayer 14 is a planarizinglayer used for leveling the topography of the substrate. Both organicand inorganic planarizing materials commonly used in photolithographicprocesses can be used in forming the underlayer 14. The thickness of theunderlayer 14 is preferably from about 50 nm to about 300 nm.

Next, a lithographic process is performed over the mask layer 16 tocreate a trench opening 18 in the mask layer, and the upper surface ofthe underlayer 14 is exposed through the trench opening 18. Thelithographic process involves conventional lithography and resistdevelopment steps. Specifically, the mask layer 16 is first exposed to adesired pattern of radiation (not shown). The exposed mask layer 16 isthen developed in a conventional resist developer to form the trenchopening 18 in the mask layer 16. The trench opening 18 has a width dthat ranges from about 30 nm to about 200 nm, more preferably from about40 nm to about 160 nm. It is preferred that the trench opening is abovethe line structure 12 in the substrate 10 and perpendicular to the linestructure 12, as shown in FIGS. 8A and 8B.

Optionally, but not necessarily, the interior surfaces of the trenchopening 18 are treated before the application of a layer of a blockcopolymer to adjust the surface affinities of a specific surface to thedifferent block components of the block copolymer. Specifically, one ormore surface layers are formed over the bottom surface and/or sidewallsurfaces of the trench opening 18. These surface layers can provide thedesired surface affinities for aligning the lamellar or cylindrical unitpolymeric block formed by the block copolymer layer inside the trenchopening 18.

If a surface has substantially the same surface affinity to both blockcomponents A and B of a block copolymer, such a surface is considered aneutral surface or a non-preferential surface, i.e., both blockcomponents A and B can wet such a surface. In contrast, if a surface hassignificantly different surface affinities for the block components Aand B, such a surface is then considered a preferential surface, i.e.,only one of block components A and B can wet such a surface, but theother cannot. For example, surfaces comprising one of silicon nativeoxides, silicon oxides, and silicon nitrides are preferentially wettedby PMMA block components, but not by PS block components. Therefore,such surfaces can be used as preferential surfaces for PS-b-PMMA blockcopolymers. On the other hand, a monolayer comprising a substantiallyhomogenous mixture of PS and PMMA components, such as a random PS-r-PMMAcopolymer layer, provides a neutral surface or a non-preferentialsurface for PS-b-PMMA block copolymers.

In order to form lamellar polymeric blocks that are alignedperpendicular to the bottom surface of the trench opening 18 fromPS-b-PMMA, it is desired to deposit a neutral or non-preferentialmonolayer (e.g., a substantially homogenous mixture of PS and PMMAcomponents) over the bottom surface of the trench opening 18, while thesidewall surfaces of the trench opening 18, which preferably comprisesilicon nitrides or oxides, are either left untreated or are coated witha preferential wetting material (e.g., silicon native oxides, siliconoxides, and silicon nitrides). In this manner, the lamellar polymericblocks formed from PS-b-PMMA will stand perpendicular to the bottomsurface of the trench opening 18 and also perpendicular to the uppersurface of said line structure

A thin layer of a self-assembling block copolymer 20 is applied over themask layer 16, including the trench opening 18, as shown in FIGS. 9A and9B. The block copolymer layer 20 preferably has a thickness that rangesfrom about 10 nm to about 50 nm, more preferably from about 15 nm toabout 45 nm.

In a preferred embodiment, the block copolymer layer 20 is a diblockcopolymer comprising a first and a second polymeric block components Aand B with a molecular weight ratio ranging from about 60:40 to about40:60. More preferably, the block copolymer layer 20 is a PS-b-PMMAblock copolymer with a PS:PMMA molecular weight ratio ranging from about60:40 to about 40:60. Such a PS-b-PMMA block copolymer, when applied andannealed on a planar surface, self-assembles into an ordered array ofPMMA lamellae in a PS matrix. However, because of the trench opening 18of the width d in the mask layer 16, annealing of the block copolymerlayer 20 results in only a single PMMA lamella 20A embedded in a PSmatrix 20B inside the trench opening 18, as shown in FIGS. 10A and 10B.The PMMA lamella 20A has a width w which is smaller than the width d andranges from about 5 nm to about 60 nm, preferably from about 10 nm toabout 50 nm.

Next, the single lamella 20A is selectively removed to form the singleopening 22 of the width w, as shown in FIGS. 11A and 11B. For example,when the block copolymer layer 20 is a PS-b-PMMA block copolymer, thesingle lamella 20A can be selectively removed by immersing the entirestructure as shown in FIGS. 10A and 10B in an acetic acid aqueoussolution containing about 62% of acetic acid for a duration of about 1minute.

The single opening 22 is then used as a mask in an etch transfer processto form an opening 24 in the line structure 12, exposing the uppersurface of the substrate 10, as shown in FIGS. 12A and 12B. The etchtransfer process may involve one or more dry or wet etch steps. It ispossible that the entire or part of the block copolymer layer 20, themask layer 16 and the underlayer 14 are removed during the etch transferprocess.

Any remaining block copolymer layer 20, mask layer 16 and underlayer 14after performing the etch process is stripped from the substrate,exposing the line structure 12 and the upper surface of the substrate 10not covered by the line structure 12, as shown in FIGS. 13A and 13B. Theopening 24 cuts the line structure 12 into two lines 12A and 12B. Thetip-to-tip spacing between these two lines 12A and 12B is thus the widthof the opening 24. Since the single opening 22 has a width w in therange from about 5 nm to about 60 nm, preferably from about 10 nm toabout 50 nm, the width of the opening 24 is also in the similar range.Such a small tip-to-tip spacing between these two lines 12A and 12Bcannot be formed by the conventional lithography techniques.

FIGS. 14A-23B are cross-sectional and top views that illustrateexemplary processing steps for reducing tip-to-tip spacing between linesaccording to another embodiment of the present invention. Thisembodiment involves many steps that are the same as those in theprevious embodiment, as illustrated in FIGS. 5A-13B.

FIG. 14A shows the cross-sectional view of a substrate 10 with a linestructure 12 on it. The cross-section site is across the line structure,as shown in FIG. 14B.

A first mask layer 15 is formed over the substrate 10 and a second masklayer 17 is formed over the first mask layer 15, as shown in FIGS. 15Aand 15B. The first mask layer 15 may comprise any suitable maskmaterial, such as an oxide, nitride, or oxynitride, and it can bedeposited by well known techniques such as chemical vapor deposition(CVD), plasma-assisted CVD, atomic layer deposition (ALD), evaporation,reactive sputtering, chemical solution deposition and other likedeposition processes. Preferably, the first mask layer 15 comprisessilicon nitride and is deposited by a CVD process.

The second mask layer 17 may comprise any suitable organic or inorganicphotosensitive materials that can be patterned by conventionallithography techniques. In a preferred embodiment, the second mask layer17 is a photoresist. The second mask layer 17 may be applied byvirtually any standard means including spin coating. The second masklayer 17 may be baked (PAB) to remove any solvent and improve thecoherence of the mask layer. The preferred range of the PAB temperatureis from about 70° C. to about 150° C., more preferably from about 90° C.to about 130° C. A typical bake time is from about 60 seconds to about90 seconds. The preferred range of thickness of the second mask layer 17is from about 20 nm to about 400 nm, more preferably from about 50 nm toabout 300 nm.

Optionally, but not necessarily, an underlayer 14 may be applied overthe substrate 10 with the line structure 12 before the first mask layer15 is formed, as shown in FIGS. 16A and 16B.

Next, a lithographic process is performed over the second mask layer 17to create a trench opening 18 in the mask layer, and the upper surfaceof the first mask layer 15 is exposed through the trench opening 18. Thelithographic process involves conventional lithography and resistdevelopment steps. The trench opening 18 has a width d that ranges fromabout 30 nm to about 200 nm, more preferably from about 40 nm to about160 nm. It is preferred that the trench opening is above the linestructure 12 in the substrate 10 and perpendicular to the line structure12, as shown in FIGS. 17A and 17B.

Optionally, but not necessarily, the interior surfaces of the trenchopening 18 are treated before the application of a layer of a blockcopolymer to adjust the surface affinities of a specific surface to thedifferent block components of the block copolymer, as described in theprevious embodiment.

A thin layer of a self-assembling block copolymer 20 is applied over thesecond mask layer 17, including the trench opening 18, as shown in FIGS.18A and 18B. The block copolymer layer 20 preferably has a thicknessthat ranges from about 10 nm to about 50 nm, more preferably from about15 nm to about 45 nm.

In a preferred embodiment, the block copolymer layer 20 is a diblockcopolymer comprising a first and a second polymeric block components Aand B with a molecular weight ratio ranging from about 60:40 to about40:60. More preferably, the block copolymer layer 20 is a PS-b-PMMAblock copolymer with a PS:PMMA molecular weight ratio ranging from about60:40 to about 40:60. Because of the trench opening 18 of the width d inthe second mask layer 17, annealing of the block copolymer layer 20results in only a single PMMA lamella 20A embedded in a PS matrix 20Binside the trench opening 18, as shown in FIGS. 19A and 19B. The PMMAlamella 20A has a width w which is smaller than the width d and rangesfrom about 5 nm to about 60 nm, preferably from about 10 nm to about 50nm.

The single lamella 20A is selectively removed to form the single opening22 of the width w in the matrix 20B, as shown in FIGS. 20A and 20B.

The single opening 22 is then used as a mask in a first etch transferprocess to form an opening 23 in the first mask layer 15, as shown inFIGS. 21A and 21B. The first etch transfer process may involve one ormore dry or wet etch steps. It is possible that the entire or part ofthe block copolymer layer 20 and the second mask layer 17 are removedduring the etch transfer process.

In a second etch transfer process, the opening 23 is used as a mask toform an opening 24 in the line structure 12, exposing the upper surfaceof the substrate 10, as shown in FIGS. 22A and 22B. The etch transferprocess may involve one or more dry or wet etch steps. It is possiblethat the entire or part of the block copolymer layer 20, the second masklayer 17, the first mask layer 15 and the underlayer 14 are removedduring the etch transfer process.

Any remaining block copolymer layer 20, the second mask layer 17, thefirst mask layer 15 and the underlayer 14 after performing the etchprocess is stripped from the substrate, exposing the line structure 12and the upper surface of the substrate 10 not covered by the linestructure 12, as shown in FIGS. 23A and 23B. As described in theprevious embodiment, the opening 24 cuts the line structure 12 into twolines 12A and 12B. The tip-to-tip spacing between these two lines 12Aand 12B is thus the width of the opening 24 which ranges from about 5 nmto about 60 nm, preferably from about 10 nm to about 50 nm.

While the present invention has been particularly shown and describedwith respect to preferred embodiments, it will be understood by thoseskilled in the art that the foregoing and other changes in forms anddetails may be made without departing from the spirit and scope of theinvention. It is therefore intended that the present invention not belimited to the exact forms and details described and illustrated butfall within the scope of the appended claims.

1. A method for reducing tip-to-tip spacing between lines comprising:providing a substrate and a line structure in said substrate; forming amask layer over said substrate; performing a lithographic process oversaid mask layer to create a trench opening of a width d in said masklayer, wherein said trench opening is above said line structure in saidsubstrate and substantially perpendicular to said line structure;applying a layer of a block copolymer over said mask layer, wherein saidblock copolymer comprises at least first and second polymeric blockcomponents A and B respectively that are immiscible with each other;annealing said block copolymer layer to form a single unit polymer blockof a width or a diameter w inside said trench opening, wherein w<d, andwherein said single unit polymer block comprises said polymeric blockcomponent B and is embedded in a polymeric matrix that comprises saidfirst polymeric block component A; selectively removing said secondpolymeric block component B to form a single opening of a width or adiameter w in said polymeric matrix inside said trench opening; andperforming an etch transfer process using said single opening as a maskto form a third opening in said line structure in said substrate,wherein said third opening cuts said line structure into two lines. 2.The method of claim 1, further comprising forming an underlayer oversaid substrate, before forming said mask layer.
 3. The method of claim2, further comprising stripping any remaining block copolymer layer,mask layer and underlayer, after said etch transfer process.
 4. Themethod of claim 1, wherein said annealing is performed at a temperaturefrom about 130° C. to about 230° C.
 5. The method of claim 4, whereinsaid annealing is performed from about 40 minutes to about 80 minutes.6. The method of claim 1, wherein said block copolymer layer has athickness from about 15 nm to about 45 nm.
 7. The method of claim 1,wherein said block copolymer, when applied and annealed on a planarsurface, self-assembles into an ordered array of multiple structuralunits comprising said polymeric block component B embedded in apolymeric matrix comprising said first polymeric block component A,wherein each of said multiple structural units has said width ordiameter w, wherein said multiple structural units are spaced apart fromeach other in said ordered array by a distance s, and wherein 0.6(w+s)<d<1.5 (w+s).
 8. The method of claim 7, wherein w ranges from about10 nm to about 50 nm and s ranges from about 10 nm to about 60 nm, andwherein d ranges from about 40 nm to about 160 nm.
 9. The method ofclaim 1, wherein said block copolymer comprises said first and secondpolymeric block components A and B, respectively, at a weight ratio offrom about 60:40 to about 40:60, and wherein the single unit polymerblock comprises a lamella that stands perpendicular to the upper surfaceof said line structure.
 10. The method of claim 1, wherein said blockcopolymer is a diblock copolymer selected from the group consisting ofpolystyrene-block-polymethylmethacrylate (PS-b-PMMA),polystyrene-block-polyisoprene (PS-b-PI),polystyrene-block-polybutadiene (PS-b-PBD),polystyrene-block-polyvinylpyridine (PS-b-PVP),polystyrene-block-polyethyleneoxide (PS-b-PEO),polystyrene-block-polyethylene (PS-b-PE),polystyrene-block-polyorganosilicate (PS-b-POS),polystyrene-block-polyferrocenyldimethylsilane (PS-b-PFS),polyethyleneoxide-block-polyisoprene (PEO-b-PI),polyethyleneoxide-block-polybutadiene (PEO-b-PBD),polyethyleneoxide-block-polymethylmethacrylate (PEO-b-PMMA),polyethyleneoxide-block-polyethylethylene (PEO-b-PEE),polybutadiene-block-polyvinylpyridine (PBD-b-PVP), andpolyisoprene-block-polymethylmethacrylate (PI-b-PMMA).
 11. The method ofclaim 1, wherein the tip-to-tip spacing of said two lines isapproximately w.
 12. The method of claim 1, wherein said mask layer is aphotoresist.
 13. The method of claim 1, wherein said line structure is agate line structure.
 14. A method for reducing tip-to-tip spacingbetween lines comprising: providing a substrate and a line structure insaid substrate; forming a first mask layer over said substrate; forminga second mask layer over said first mask layer; performing alithographic process over said second mask layer to create a trenchopening of a width d in said second mask layer, wherein said trenchopening is above said line structure in said substrate and substantiallyperpendicular to said line structure; applying a layer of a blockcopolymer over said second mask layer, wherein said block copolymercomprises at least first and second polymeric block components A and Brespectively that are immiscible with each other; annealing said blockcopolymer layer to form a single unit polymer block of a width or adiameter w inside said trench opening, wherein w<d, and wherein saidsingle unit polymer block comprises said polymeric block component B andis embedded in a polymeric matrix that comprises said first polymericblock component A; selectively removing said second polymeric blockcomponent B to form a single opening of a width or a diameter w in saidpolymeric matrix inside said trench opening; performing a first etchtransfer process using said single opening as a mask to form a thirdopening in said first mask layer; and performing a second etch transferprocess using said third opening in said first mask layer as a mask toform a fourth opening in said line structure in said substrate, whereinsaid fourth opening cuts said line structure into two lines.
 15. Themethod of claim 14, further comprising forming an underlayer over saidsubstrate, before forming said first mask layer.
 16. The method of claim15, further comprising stripping any remaining block copolymer layer,first mask layer, second mask layer and underlayer, after said secondetch transfer process.
 17. The method of claim 14, wherein saidannealing is performed at a temperature from about 130° C. to about 230°C.
 18. The method of claim 17, wherein said annealing is performed fromabout 40 minutes to about 80 minutes.
 19. The method of claim 14,wherein said block copolymer layer has a thickness from about 15 nm toabout 45 nm.
 20. The method of claim 14, wherein said block copolymer,when applied and annealed on a planar surface, self-assembles into anordered array of multiple structural units comprising said polymericblock component B embedded in a polymeric matrix comprising said firstpolymeric block component A, wherein each of said multiple structuralunits has said width or diameter w, wherein said multiple structuralunits are spaced apart from each other in said ordered array by adistance s, and wherein 0.6 (w+s)<d<1.5(w+s).
 21. The method of claim20, wherein w ranges from about 10 nm to about 50 nm and s ranges fromabout 10 nm to about 60 nm, and wherein d ranges from about 40 nm toabout 160 nm.
 22. The method of claim 14, wherein said block copolymercomprises said first and second polymeric block components A and B,respectively, at a weight ratio of from about 60:40 to about 40:60, andwherein the single unit polymer block comprises a lamella that standsperpendicular to the upper surface of said line structure.
 23. Themethod of claim 14, wherein said block copolymer is a diblock copolymerselected from the group consisting ofpolystyrene-block-polymethylmethacrylate (PS-b-PMMA),polystyrene-block-polyisoprene (PS-b-PI),polystyrene-block-polybutadiene (PS-b-PBD),polystyrene-block-polyvinylpyridine (PS-b-PVP),polystyrene-block-polyethyleneoxide (PS-b-PEO),polystyrene-block-polyethylene (PS-b-PE),polystyrene-block-polyorganosilicate (PS-b-POS),polystyrene-block-polyferrocenyldimethylsilane (PS-b-PFS),polyethyleneoxide-block-polyisoprene (PEO-b-PI),polyethyleneoxide-block-polybutadiene (PEO-b-PBD),polyethyleneoxide-block-polymethylmethacrylate (PEO-b-PMMA),polyethyleneoxide-block-polyethylethylene (PEO-b-PEE),polybutadiene-block-polyvinylpyridine (PBD-b-PVP), andpolyisoprene-block-polymethylmethacrylate (PI-b-PMMA).
 24. The method ofclaim 14, wherein the tip-to-tip spacing of said two lines isapproximately w.
 25. The method of claim 14, wherein said second masklayer is a photoresist.
 26. The method of claim 14, wherein said linestructure is a gate line structure.